A number of epidemiological studies have observed an inverse association between
phytoestrogens and risk of certain hormonally dependent
cancers. We undertook an exploratory analysis of the relationship between specific
phytoestrogens and premalignant cervical lesions. A case-control study of 122 women with histologically confirmed cervical
squamous intraepithelial lesions (SILs) of the cervix and 183 cytologically normal controls was conducted from 1992 to 1996 in Honolulu, Hawaii. A cervical cell sample was obtained for human papillomavirus (HPV) testing. Dietary information was collected using a structured survey, and a fasting blood sample was taken for measurement of five isoflavonoids (
genistein,
glycitein,
daidzein,
O-desmethylangolensin, and
equol), two
flavonoids (
hesperetin and
naringenin), and two
lignans (
enterodiol and
enterolactone). Plasma levels of
equol and
enterodiol were positively associated with cervical SIL risk: odds ratio, OR = 6.5; 95% confidence interval, CI = 1.4-29.2; P for trend = 0.02 and OR = 2.7; 95% CI = 1.1-6.3; P for trend = 0.01, respectively, for the highest relative to the lowest quartile level after adjustment for age, race/ethnicity,
HPV infection, cigarette smoking, alcohol drinking, and lifetime number of sexual partners. A nonsignificant positive association with cervical SIL risk was observed for plasma
enterolactone. Consistent with the relationships observed for the plasma
lignans, dietary sources of
lignans, including garlic and taro leaves/ong choy/marunggay, were positively associated with cervical SIL risk. A positive association was also suggested for other
lignan sources such as seaweed, onions, grapefruit, and seeds. This is the first study to observe a positive association between specific
phytoestrogens and premalignancies of the cervix. The results of this investigation should be considered preliminary and need to be verified in larger, prospective studies.